1. Field of the Invention
This invention relates to method for making urethane molded products for polishing pad which are provided for polishing articles to be polished such as semiconductor devices, and also to urethane molded products for polishing pad.
2. Description of the Prior Art
Polishing pads used for semiconductor devices and glasses are known, including those pads of the porous non-woven fabric type obtained by applying a polyurethane solution to a non-woven fabric as set out in Japanese Laid-open Patent No. 64-58475 and of the foamed polyurethane type which is obtained by wet molding of a polyurethane solution. Both types of pads have a structure which is provided with cellular holes on the surface thereof, and thus, are a good property of holding an article to be polished at the time of polishing and are able to favorably retain a supplied grain solution (polishing slurry) therein. However, these pads are disadvantageous in that they are too soft to cause compressive deformation on use, poor in flatness of the surface of a polished article obtained by polishing, and short in life of the polishing pad.
In recent years, as semiconductor devices are highly integrated, an interconnection pattern on a substrate is more densified, under which there is a strong demand for flatness on a substrate surface as influencing the transfer of a pattern. In order to provide a more flattened wafer surface of a semiconductor substrate, there has been adopted a chemical mechanical polishing process (abbreviated as CMP process) wherein a chemical function and a mechanical function are combined. It has been demanded to develop a polishing pad which is suitably applicable to such the CMP process.
For instance, Japanese Laid-open Patent No. Hei 8-500622 discloses a polishing pad which comprises a plurality of polymeric fine elements, such as expanded microballoons, in a polyurethane matrix. The pad has a high surface hardness, so that it is more unlikely to cause compressive deformation than such a non-woven or foamed polyurethane-type polishing pad as mentioned above, thereby ensuring a high polishing rate and a good flatness. However, only one type of the expanded microballoons are mentioned as the polymeric fine elements used. When used as a polishing pad, the cells derived from the microballoons are allowed to open at the surface of the polishing pad, and abrasive grains are held at the opened cells. Nevertheless, the holding or retaining property of abrasive grains or the like with the cells alone is not satisfactory. Accordingly, there is a demand for a polishing pad which is improved in the retaining property and ensures improved polishing rate and flatness.
Further, once expanded microballoons have the drawback that they are small in specific gravity and have a great difference in specific gravity with an isocyanate-terminated urethane prepolymer, so that when mixed, they are liable to separate from each other, resulting in a poor dispersion of high viscosity, and that when such microballoons are mixed with an amine compound under agitation, air-mixing is caused. Moreover, when a microballoon-incorporated isocyanate-terminated urethane prepolymer and an amine compound are subjected to cast molding in a mold, the expanded microballoons are floated during a time before curing of the polyurethane resin, thus presenting the problem that a uniformly dispersed polishing pad cannot be obtained.
An object of the invention is to provide the urethane molded products for use as a polishing pad, which comprises two types of cells of different sizes, created by expanded microballoons and water, in the urethane molded products, so that a polishing pad obtained by slicing the resultant urethane molded products into pieces is improved in polishing characteristics, with a reduced variation in the polishing characteristics among polishing pads.
A further object of the invention is to provide the urethane molded products for use as a polishing pad wherein two different sizes of cells are formed in the urethane molded products, including one type of cells formed by expanding non-expanded, thermally expandable microspheres and the other type of cells having a larger size than the former cells and formed with water.
According to one embodiment of the invention, there is provided a method for making urethane molded products for polishing pad which comprises mixing a mixture of expanded microballoons (A1), an isocyanate-terminated urethane prepolymer (B), and an active hydrogen-containing compound (C) with 0.005 to 0.5 wt %, based on the mixture, of water (D), and forming cells created by the action of the water (D) along with cells derived from the expanded microballoons (A1) in the resultant molded products wherein the expanded microballoons (A1) are pre-mixed with the isocyanate-terminated urethane prepolymer (B) and/or the active hydrogen-containing compound (C) . It is preferred that the expanded microballoons are present in an amount of 0.1 to 10 parts by weight relative to 100 parts by weight of the total of the isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C). The urethane molded products for polishing pad obtained according to this embodiment comprises expanded microballoons (A1) and cells formed by means of water (D) therein.
According to another embodiment of the invention, there is also provided a method for making urethane molded products for polishing pad which comprises mixing a mixture of non-expanded, thermally expandable microspheres (A2), an isocyanate-terminated urethane prepolymer (B), and an active hydrogen-containing compound (C) with 0.005 to 0.5 wt %, based on the mixture, of water (D), and expanding the non-expanded, thermally expandable microspheres (A2) by application of heat of reaction and heat from outside and also forming cells created by the action of the water (D) wherein the non-expanded, thermally expandable microspheres (A2) are pre-mixed with the isocyanate-terminated urethane prepolymer (B) and/or the active hydrogen-containing compound (C) . Preferably, the non-expanded, thermally expandable microspheres are present in an amount of 0.1 to 10 parts by weight relative to 100 parts by weight of the total of the isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C). The urethane molded products for polishing pad obtained according to this second embodiment of the invention comprises microballoons (A1) expanded by application of heat at the time of urethane molding and cells formed by means of water (D) therein.
In this invention, the active hydrogen-containing compound should preferably consist of a diamine compound (C1) or a mixture of the diamine compound (C1) and a low molecular weight diol (C2) having a molecular weight of 500 to 1000.
As disclosed in Japanese Laid-open Patent No. Sho 57-137323 and the like, the expanded microballoons (A1) used in the present invention are obtained by thermal expansion of non-expanded, thermally expandable microspheres which individually have a low boiling hydrocarbon, such as, for example, isobutane, pentane, isopentane, petroleum ether or the like, at a center thereof and a shell encapsulating the hydrocarbon therein and made of a thermoplastic resin such as, for example, an acrylonitrile-vinylidene chloride copolymer, an acrylonitrile-methyl methacrylate copolymer, a vinyl chloride-ethylene copolymer or the like. When heated, the low boiling hydrocarbon existing at the center of each microspheres is vaporized and gasified to cause the shell portion to be softened thereby providing microballoons (A1) having a gas encapsulated therein. The expanded microballoons (A1) preferably have a size of 10 to 100 xcexcm. If the size of the expanded microballoons (A1) is smaller than 10 xcexcm, an appreciable polishing effect may not be expected. On the contrary, when the size is larger than 100 xcexcm, the resultant urethane molded products for polishing pad unfavorably lowers in hardness.
The isocyanate-terminated urethane prepolymer (B) used in the invention is a reaction product obtained from a polyol or a mixture of a polyol and a low molecular weight diol and an organic diisocyanate compound under ordinarily employed reaction conditions. Examples of the organic diisocyanate compound include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4xe2x80x2-diphenylmethane diisocyanate, naphthalene-1,5-diisocyanate, tolidine diisocyanate, para-phenylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate and the like. These may be used singly or in combination of two or more.
The polyol for reaction with an organic diisocyanate compound include, for example, polyether polyols such as poly(oxytetramethylene)glycol, poly(oxypropylene)glycol and the like, polycarbonate polyols, polyester polyols, and the like.
As the polyol, there may be used mixtures of low molecular weight diols such as, for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol and the like.
The active hydrogen-containing compound (C) used to polymerization reaction of the isocyanate-terminated urethane prepolymer (B) include, for example, diamine compound (C1) such as 3,3xe2x80x2-dichloro-4,4xe2x80x2-diaminodiphenylmethane, chloroaniline-modified dichlorodiaminodiphenylmethane, 3,5-bis(methylthio)-2,4-toluenediamine, 3,5-bis(methylthio)-2,6-toluenediamine and the like. Moreover, the active hydrogen-containing compounds (C) include, aside from the above-indicated diamine compound (C1), their mixtures with low molecular weight diol (C2) having the molecular weight in the range of 500 to 1000 such as, for example, polyether glycols such as poly(oxytetramethylene)glycol, poly(oxypropylene)glycol and the like, polycarbonate glycols, polyester glycols and the like.
In the practice of the invention, the expanded microballoons (A1) are added to and mixed with the isocyanate-terminated urethane prepolymer (B) and/or the active hydrogen-containing compound (C) and are reacted with each other. More particularly, there may be used several methods including a method wherein a dispersion, obtained by adding the expanded microballoons (A1) to the isocyanate-terminated urethane prepolymer (B), is mixed with the active hydrogen-containing compound (C) to which expanded microballoons (A1) are not added, a method wherein the isocyanate-terminated urethane prepolymer (B), to which expanded microballoons (A1) are not added, is mixed with a dispersion of the expanded microballoons (A1) in the active hydrogen-containing compound (C), and a method wherein dispersions of the expanded microballoons (A1) in the isocyanate-terminated urethane prepolymer (B) and also in the active hydrogen-containing compound (C) are mixed together.
The amount of the expanded microballoons (A1) is in the range of 0.1 to 10 parts by weight, preferably 2 to 5 parts by weight, per 100 parts by weight of the total of the isocyanate-terminated urethane polymer (B) and the active hydrogen-containing compound (C). If the amount is less than the above range, the resulting polishing pad lowers in polishing characteristics such as the polishing rate and the flatness. On the other hand, when the amount is larger, the hardness of the polishing pad unfavorably lowers.
In the practice of the invention, the dispersion of the expanded microballoons (A1) in an isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C) having not expanded microballoons (A1) therein, or isocyanate-terminated urethane prepolymer (B), to which expanded microballoons (A1) are not added, and the dispersion of the expanded microballoons (A1) in the active hydrogen-containing compound (C), or the dispersion of the expanded microballoons (A1) in the isocyanate-terminated urethane prepolymer (B) and the dispersion of the expanded microballoons (A1) in the active hydrogen-containing compound (C) may be charged into a mixer having three charge ports from the two charge ports, simultaneously with water (D) being charged from the third charge port of the mixer. Where a mixer having two charge ports is used, water may be added to the active hydrogen-containing compound (C), or to a dispersion of the expanded microballoons (A1) in the active hydrogen-containing compound (C), followed by charge into a mixer.
The thus added water (D) is mixed in the mixer and is vaporized during the course of obtaining the urethane molded products wherein the resultant cells are contained in the molded product.
The cells formed by the action of the water (D) have a size of 100 to 800 xcexcm, which is approximately 10 times as great as the size of the expanded microballoons (A1). The number of the cells is {fraction (1/10)} to {fraction (1/20)} of that of the microballoons. When the polishing pad obtained from such the urethane molded products is used for semiconductor polishing, there are provided two types of cells having different sizes in the surface of the polishing pad, including the cells formed by rendering the expanded microballoons (A1) opened and the cells ascribed to the water (D). In addition, the urethane pad is so abraded during polishing that two types of fresh cell holes invariably develop. This leads to a large amount of abrasive grains to be held in or on the polishing pad, thereby improving polishing characteristics such as the polishing rate and the flatness. Moreover, because the surface of the polishing pad, which is brought into contact with a surface to be polished, is invariably kept clean, thereby providing an effect of preventing the surface to be polished from damaging.
The amount of the water (D) charged into the mixer is in the range of 0.005 to 0.5 wt %, preferably 0.02 to 0.05 wt %, based on the total of the expanded microballoons (A1), the isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C).
If the amount of the water (D) is less than 0.005 wt %, the cells created by the water (D) are reduced in number, so that the improvement in polishing rate and the effect of preventing a surface to be polished from damaging cannot be expected as desired. In contrast, if the amount is larger than 0.5 wt %, a ratio of cells having a size greater than that of the expanded microballoons (A1) becomes greater in the urethane molded products. Eventually, the hardness of the molded products lowers. Additionally, the resultant polishing pad is roughened on or in the surface thereof, s, that although the polishing rate is improved, the flatness unfavorably degrades.
The reaction solution or mixture from the mixer is charged into a mold preheated to 90 to 120xc2x0 C. followed by clamping the mold and primary curing at 90 to 120xc2x0 C. for about 30 minutes. Further, after removal from the mold, the molded product is placed in a heating oven and subjected to secondary curing at 90 to 120xc2x0 C. for 5 to 20 hours.
The urethane molded products for polishing pad obtained according to the method of the invention has two types of cells having different sizes, which are, respectively, formed on the basis of the expanded microballoons (A1) and the water (D), and exhibits such properties as set out before. When the molded product is sliced into pieces, there can be obtained polishing pads having good polishing characteristics.
As mentioned above, pollshing pads can be obtained by slicing the urethane molded products into a desired thickness and cutting the resultant pieces as having a desired size. In this connection, the manner of slicing and cutting and whether or not desired grooves are formed in the surface of the polishing pad are not restricted.
In the second embodiment of the invention, non-expanded, thermally expandable microspheres (A2) are those disclosed, for example, in Japanese Laid-open Patent No. Sho 57-137323, like the expanded microballoons (A1) set out hereinbefore. When such microspheres (A2) are heated, a low boiling hydrocarbon existing at the central portion thereof is vaporized and gasified to cause a shell of the microspheres to be softened, tnereby providing expanded hollow microballoons (A) encapsulating the gas therein.
The non-expanded, thermally expandable microspheres (A2) preferably have a size of 5 to 30 xcexcm. When expanded by application of heat, the size increases to 10 to 100 xcexcm. If the non-expanded, thermally expandable microspheres (A2) has a size larger than 30 xcexcm, the size after the expansion becomes too large, which is unfavorable for the urethane molded products for polishing pad. In addition, the non-expanded, thermally expandable microspheres (A2) should preferably have a specific gravity close to that of an isocyanate-terminated urethane prepolymer (B) used in order to avoid any possible trouble on use.
The non-expanded, thermally expandable microspheres (A2) is added to and mixed with the isocyanate-terminated urethane prepolymer (B) and/or the active hydrogen-containing compound (C), followed by reaction thereof. The isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C) are used as like as those set out in the first embodiment. More particularly, a dispersion of the non-expanded, thermally expandable microspheres (A2) in the isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C), to which non-expanded, thermally expandable microspheres (A2) are not added, may be mixed. Alternatively, there may be used another method wherein the isocyanate-terminated urethane prepolymer (B), to which any non-expanded, thermally expandable microspheres (A2) are not added, and a dispersion of the non-expanded, thermally expandable microspheres (A2) in the active hydrogen-containing compound (C) are mixed. Still alternatively, a further method may be used in which a dispersion of the non-expanded, thermally expandable microspheres (A2) in the isocyanate-terminated urethane prepolymer (B) and a dispersion of the non-expanded, thermally expandable microspheres (A2) in the active hydrogen-containing compound (C) are mixed.
The amount of the non-expanded, thermally expandable microspheres (A2) is in the range of 0.1 to 10 parts by weight, preferably 2 to 5 parts by weight, per 100 parts by weight of the total of the isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C). If the amount is less than the above range, the resulting polishing pad lowers polishing characteristics such as the polishing rate and the flatness. On the other hand, when the amount is larger, the hardness of the polishing pad unfavorably lowers.
In the practice of the invention, like the foregoing embodiment, the dispersion of the non-expanded, thermally expandable microspheres (A2) in an isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C), to which any non-expanded, thermally expandable microspheres (A2) are not added, or isocyanate-terminated urethane prepolymer (B), to which any non-expanded, thermally expandable microspheres (A2) are not added, and the dispersion of the non-expanded, thermally expandable microspheres (A2) in the active hydrogen-containing compound (C), or the dispersion of the non-expanded, thermally expandable microspheres (A2) in the isocyanate-terminated urethane prepolymer (B) and the dispersion of the non-expanded, thermally expandable microspheres (A2) in the active hydrogen-containing compound (C) may be charged from two charge ports of a mixer having three charge ports, simultaneously with water (D) being charged from the third charge port of the mixer. Where a mixer having two charge ports is used, water may be added to the active hydrogen-containing compound (C), or to a dispersion of the non-expanded, thermally expandable microspheres (A2) in the active hydrogen-containing compound (C), followed by charge into a mixer.
When the respective dispersions are used in the method of the invention, it is preferred to keep them at a temperature of about 100xc2x0 C. or below prior to charge into a mixer and also to keep them at a temperature lower than an expanding and foaming temperature of the non-expanded, thermally expandable microspheres (A2). The non-expanded, thermally expandable microspheres (A2) start to expand by heat of reaction generated at the time when the isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C) are reacted in the mixer.
The added water (D) is mixed in the mixer and is vaporized or gasified during the course of obtaining the urethane molded products wherein the resultant cells are contained or confined in the molded products.
The cells formed by the action of the water (D) have a size of 100 to 800 xcexcm, which is approximately 10 times as great as the size of the expanded hollow microballoons (A). The number of the cells is {fraction (1/10)} to {fraction (1/20)} of that of the microspheres. When the polishing pad obtained from such the urethane molded products is used for semiconductor polishing, there are provided two types of cells having different sizes in the surfaces of the polishing pad. As a consequence, the urethane pad is so abraded during polishing that two types of fresh cell holes invariably develop. This leads to a large amount of abrasive grains to be held on the polishing pad, thereby improving polishing characteristics such as the polishing rate and the flatness. Moreover, because the surface of the polishing pad, which is brought into contact with a surface to be polished, is invariably kept clean, there can be obtained an effect of preventing the surface to be polished from damaging.
The amount of the water (D) charged into the mixer is in the range of 0.005 to 0.5 wt %, preferably 0.02 to 0.05 wt %, based on the total of the non-expanded, thermally expandable microspheres (A2), the isocyanate-terminated urethane prepolymer (B) and the active hydrogen-containing compound (C).
If the amount of the water (D) is less than 0.005 wt %, the cells created by the water (D) are reduced in number, so that the improvement in polishing rate and the effect of preventing a surface to be polished from damaging due to polishing dust cannot be expected as desired. On the contrary, if the amount is larger than 0.5 wt %, a ratio of cells having a size greater than that of the expanded hollow microballoons (A) becomes greater in the urethane molded product. Eventually, the hardness of the molded product lowers. Additionally, the resultant polishing pad is roughened on or in the surfaces thereof, so that although the polishing rate is improved, flatness is unfavorably poor.
The polymer solution or mixture from the mixer is charged into a mold heated to 90 to 120xc2x0 C. followed by clamping the mold and primary curing at 90 to 120xc2x0 C. for about 30 minutes. Further, after removal from the mold, the molded product is placed in a heating oven and subjected to secondary curing at 90 to 120xc2x0 C. for 5 to 20 hours. The heating from outside permits the non-expanded, thermally expandable microspheres (A2) to be completely expanded to provide thermally expanded hollow microballoons (A) in the urethane molded product.
The urethane molded product for polishing pad obtained in the method of the second embodiment of the invention has two types of cells having different sizes, which are, respectively, formed on the basis of the thermally expanded hollow microballoons (A) and the water (D), and exhibits such properties as set out before. When the molded product is sliced into pieces, there can be obtained polishing pads having good polishing characteristics.
The urethane molded products for polishing pad obtained by the method according to the this invention has two types of cells having different sizes dispersed therein, which are, respectively, formed on the basis of the expanded microballoons and the water or the non-expanded, thermally expandable microspheres and the water. When the urethane molded product is sliced and cut into polishing pads and they are used for semiconductor polishing, the amount of abrading grains retained in or on the polishing pad becomes large. Thus, the polishing pads exhibits excellent polishing characteristics such as a polishing rate, flatness and the like, along with the effect of remarkably improving a variation in the polishing characteristics among the polishing pads.